# fd(4)

## NAME

         fd - floppy disk

## DESCRIPTION

         The fd* devices refer to the Floppy  disk  driver  using  the  NEC  PD765
         floppy  disk controller.  These diskettes are arrays of 512 byte sectors,
         although Minix always works with two sectors at a time due  to  its  1024
         byte  block  size.   You  can  read or write any number of bytes however,
         Minix takes care of cutting and pasting incomplete blocks together.

         The driver is normally configured for two floppy  disk  devices  fd0  and
         fd1.  It can handle two more, but it is unlikely that the average PC can.

         On the first access to an fd device (by open(2) or mount(2)), the  driver
         will  execute  a series of read tests to determine the floppy type.  This
         works ok for all floppy types except the true 360k type,  because  it  is
         indistinguishable  from  the 720k type.  This only means that the size of
         the floppy is not estimated right.

         Bits 2-6 of the minor device number may be set to the floppy disk type to
         make  it  known  to  the  driver  what  type of diskette it is reading or
         writing.  The non-auto devices should be used for formatting, or when one
         wants  to  be  absolutely  sure that the device is accessed right.  These
         devices exist for drive 0:

             type   device   minor   media
              0      fd0      0      autodetect
              1      pc0      4      360k, 5.25"
              2      at0      8      1.2M, 5.25"
              3      qd0      12     360k in a 720k, 5.25" drive
              4      ps0      16     720k, 3.5"
              5      pat0     20     360k in a 1.2M, 5.25" drive
              6      qh0      24     720k in a 1.2M, 5.25" drive
              7      PS0      28     1.44M, 3.5"

         Type 4 may also be used for the rarely seen 720k, 5.25" floppies (type  2
         made  them  obsolete  fast.)   Note  that these "types" only describe the
         floppies from a software point of view, type 1 and 4 drives use the  same
         parameters.

         If the format bit (bit 7)  is  set,  then  the  driver  interprets  write
         commands  as  track  formatting  requests.  This is used by the format(1)
         command.

         If the type bits are set to 28, 29, 30, or 31, then  the  driver  uses  a
         partition  table  found  in  sector  0  to  partition  the  floppy.   The
         partitions of fd0 may be accessed as fd0a through fd0d.  See hd(4) for  a
         description of the partition table, and associated ioctl commands.

## FILES

         /dev/fd[0-3],  /dev/pc[0-3],  /dev/at[0-3],  /dev/qd[0-3],  /dev/ps[0-3],
         /dev/pat[0-3], /dev/qh[0-3], /dev/PS[0-3], /dev/fd[0-3][a-d]

## SEE ALSO

         format(1), hd(4), part(8).

## BUGS

         The driver does not know the size of a 360k  diskette  in  a  360k  5.25"
         drive,  because  it  uses the 720k parameters for it.  So it will happily
         try to read past the end making all kinds of interesting noises.  It's  a
         good thing these drives are practically obsolete.

         The partition table is only read when the drive motor is off and only for
         an auto or partition device.  The driver assumes that a floppy in a drive
         with a running motor can't have been replaced all of a sudden.

## AUTHOR

         Kees J. Bot (kjb@cs.vu.nl)